Anodic Film Formation on AA 2099-T8 Aluminum Alloy in Tartaric–Sulfuric Acid

The anodizing behavior of a lithium-containing aluminum alloy (AA 2099-T8) in an environmentally friendly electrolyte, namely tartaric–sulfuric acid (TSA), has been examined under potentiodynamic and potentiostatic conditions. Specifically, the dependence of the anodic film morphology and composition on the anodizing voltage was investigated. It is revealed that porous anodic films with well-defined cells were formed at relatively low voltages while porous anodic films with pores of increased dimensions and lateral porosity were formed at increased voltages. In addition, it is indicated that copper in the alloy matrix can be occluded in the anodic film material as copper-rich nanoparticles or it can be oxidized and incorporated into the film material as copper ions, depending on the anodizing voltage. In the latter case, the process is accompanied by oxygen gas generation within the film material, resulting in the lateral porosity in the anodic film. Further, the structures of the copper-rich nanoparticles have been determined and the mechanism of the formation of such nanoparticles has been discussed.